Use eBay.com's Completed and Sold Listings feature to find sale values for Matchbox collectibles. This gives a general idea of what buyers are willing to pay. Other sources include websites about Matchbox toys and collectibles, printed collectors' guides, and toy and collectibles dealers.
Values of individual items vary depending on the condition of the toy and its packaging. Various rating systems for items exist, based on paint chips, dents and other defects.
EBay gives accurate values for Matchbox toys and collectibles, as it shows you how much people have actually paid for particular items. EBay only stores values of completed and sold items for 90 days, so the prices reflect up-to-date market values.
Toy and collectibles dealers have their own websites for selling Matchbox collectibles. The prices on these websites may be higher than what you pay on eBay, as dealers may use outdated price information or may hope that an uninformed buyer pays more than the current market value.
You can also visit toy and collectibles dealers at their brick-and-mortar stores or at toy shows, They can give you a valuation on either individual items or a whole collection.
Several collectors' price guides are also available as physical printed books, such as "The Encyclopedia of Matchbox Toys" by Charlie Mack.